Interview Java Developer interview questions and answers (2026)
The Java Developer questions candidates are most often asked, covering Core Java, OOP, Collections, Multithreading, Spring Boot. Each answer is short enough to say out loud. For the full process, scenario and HR questions and a 48-hour plan, open the guide for your company below.
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- Accenture Java Developer interview questions
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- Infosys Java Developer interview questions
- TCS Java Developer interview questions
- Wipro Java Developer interview questions
Most asked Java Developer questions
How does Java achieve platform independence?
Java source is compiled into bytecode, which runs on any system that has a compatible JVM. The JVM handles execution details for that platform, so the same .class file can run on Windows, Linux, or macOS. This is why Java is often called "write once, run anywhere".
From the Accenture Java Developer guide
How does Java create a memory barrier for visibility between threads, and why does it matter?
A memory barrier ensures one thread’s writes become visible to another thread in the expected order. In Java, volatile, synchronized, and some concurrent utilities create these visibility guarantees. Without them, a thread may read stale values from cache or registers. This matters in shared state, for example when one thread publishes a flag or updates a cache entry that other threads must see immediately and consistently.
From the Amazon Java Developer guide
What is the difference between String, StringBuilder, and StringBuffer in Java?
String is immutable, so every change creates a new object. StringBuilder is mutable and faster for single-threaded string updates. StringBuffer is also mutable, but its methods are synchronized, so it is thread-safe but usually slower. In interviews, say that for repeated concatenation inside loops, StringBuilder is preferred unless multiple threads must access the same object.
From the Infosys Java Developer guide
What is the difference between == and .equals() in Java?
== compares references for objects and compares values for primitives. .equals() compares logical equality, if the class overrides it. For example, two different String objects with the same text may be equal with .equals() but not with ==. If you create your own class and want meaningful comparison, override equals() and also hashCode() so collections like HashSet and HashMap behave correctly.
From the TCS Java Developer guide
Explain how the Java memory model handles happens‑before relationships
The Java memory model defines a happens‑before order that guarantees visibility of writes to other threads. Actions like acquiring a lock, entering a synchronized block, calling a volatile write, or starting a thread create a happens‑before edge to subsequent reads. This ensures that when thread A writes to a variable and then releases a lock, thread B acquiring the same lock will see the updated value. Understanding these edges helps avoid stale data and race conditions.
From the Wipro Java Developer guide
What is the difference between checked and unchecked exceptions in Java?
Checked exceptions must be handled or declared with throws, so the compiler forces you to deal with them. Unchecked exceptions extend RuntimeException and usually indicate programming mistakes, such as bad indexing or null access. In enterprise code, checked exceptions are often used for recoverable external failures.
From the Accenture Java Developer guide
What is the difference between shallow copy and deep copy in Java?
A shallow copy duplicates the outer object but still shares references to nested objects. A deep copy creates new copies of both the outer object and everything it refers to. Shallow copy is cheaper, but changes to shared inner objects can leak across copies. Deep copy is safer when objects are mutable and each copy must be isolated, such as in request processing or defensive copying of domain objects.
From the Amazon Java Developer guide
How does the final keyword work in Java for variables, methods, and classes?
final means the value or behavior cannot be changed after definition. A final variable cannot be reassigned, though a final reference can still point to a mutable object whose contents change. A final method cannot be overridden, and a final class cannot be extended. Use it when you want safety, readability, and to prevent unintended inheritance or reassignment.
From the Infosys Java Developer guide
Why should equals() and hashCode() be overridden together?
If two objects are equal by equals(), they must return the same hashCode(). Hash-based collections use hashCode() first to find a bucket, then equals() to confirm the match. If the contract is broken, you can get duplicate entries or lookup failures in HashMap and HashSet. A safe answer is that both methods must be consistent to preserve correct behavior in collections.
From the TCS Java Developer guide
What is the purpose of the transient keyword in serialization
transient marks a field to be ignored during default serialization. When an object is written to a stream, transient fields are not saved, so their values are lost on deserialization and revert to default. Use it for sensitive data like passwords or for fields that can be recomputed, reducing serialized size and protecting security.
From the Wipro Java Developer guide
What is method overloading and method overriding?
Overloading means same method name, different parameter list, usually in the same class. Overriding means a subclass provides its own implementation of a parent method with the same signature. Overloading is resolved at compile time, while overriding is resolved at runtime.
From the Accenture Java Developer guide
How does LinkedHashMap work, and when would you use it instead of HashMap?
LinkedHashMap keeps entries in insertion order, or access order if configured that way, by maintaining a doubly linked list in addition to the hash table. Use it when iteration order matters, or when you want simple LRU-style behavior. It has slightly more overhead than HashMap, so choose it only when predictable ordering or cache-like eviction is useful.
From the Amazon Java Developer guide
What is the difference between an abstract class and an interface in Java?
An abstract class can hold state, constructors, abstract methods, and concrete methods. An interface mainly defines a contract, and a class can implement multiple interfaces. In modern Java, interfaces can also have default and static methods, but they still do not replace an abstract class when shared state or base implementation is needed. A good answer should mention design intent, not just syntax.
From the Infosys Java Developer guide
What is the difference between ArrayList and LinkedList?
ArrayList stores elements in a dynamic array, so random access by index is fast. LinkedList stores nodes with links, so insertions and deletions in the middle can be easier, but index access is slower because it must traverse the list. In most business applications, ArrayList is used more often because read access is common and it gives better cache performance.
From the TCS Java Developer guide
Describe the difference between Stream API's map and flatMap
map applies a function to each element and returns a stream of the transformed elements, preserving the one‑to‑one relationship. flatMap applies a function that returns a stream for each element and then flattens those streams into a single continuous stream, useful when each input maps to multiple outputs, such as splitting sentences into words.
From the Wipro Java Developer guide
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